You can. I just bought my phone separately because Verizon wanted an extra $20 a month if I got the subsidized phone + contract, but I'd rather not have a contract.

You can, just pop in a Verizon SIM.

They act like you need a whitelisted IMEI, but the network doesn't actually care. The tricky part is getting a SIM activated on their network.

The store managers pretend like they can't give/sell just a SIM. They're supposed to give them to you for free, but lie to sell you a handset. You can buy them from resellers who DGAF. They also pretend you need a whitelisted IMEI to activate the SIM card, their website and in-store people enforce this rule. I've always had good luck calling their 1-800 number and playing dumb. At the very worst you can probably find an old or broken verizon phone for free/cheap and use that IMEI.